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Protractors

Engineering & Drafting

By the end of the 18th century, protractors were routinely manufactured by machinery, with the invention of dividing engines, such as Jesse Ramsden's, particularly important for enabling the precise division of a circle into fractions of angles. Makers produced protractors that read minute fractions of angles, particularly when a vernier was added to the instrument.

Mechanics or machinists also used protractors to draw designs for new types of machinery. For instance, there were several forms of limb protractors for draftsmen that both functioned as T-squares and provided angle measurement. Similarly, protractors assisted with the preparation of architectural drawings. The instruments were only displaced by the advent of computer-aided drafting in the late 20th century.

This semicircular protractor is housed in its original wooden fitted case. The case is in very poor condition, but it was originally covered with thin leather and lined with purple velvet. The case is marked: I. KERN á AARAU [/] EN SUISSE. The maker’s mark indicates the protractor was produced between 1819 and 1885 in the workshop founded by Jakob Kern (1790–1867) in Aarau, Switzerland.

Renamed Kern & Co. in 1885, the firm was highly regarded for its craftsmanship. Its products can be found in the catalogs of many 20th American manufacturers and retailers. Kern & Co. merged with the Wild Leitz group in 1988, and the plant in Aarau closed in 1991. Former employees ensured that 1,700 objects were preserved as the Kern Collection in the city museum of Aarau, Stadtmuseum Schlössli Aarau.

The protractor is made of German silver, also called nickel silver. It is graduated along the outer edge to one-quarter degree and engraved by tens from 350 to 0 to 190 in both directions, from left to right and from right to left. A center cross-plate, or horncentre, contains crosshairs to assist with placing the protractor on a drawing. A movable arm attached to the center contains a vernier scale that allows the user to read angles to one minute of arc. The number 8 is stamped on the back of the vernier arm. The arm also has a blade-like extension three inches long. The arm was lengthened and squared off in versions sold in the 20th century. In 1909, Keuffel & Esser sold a similar protractor in a mahogany case for $19.25.

This protractor was owned by the renowned American designer of steam engines, Erasmus Darwin Leavitt Jr. (1836–1916), and donated by his granddaughter, Margaret van D. Rice.

This German silver semicircular protractor bears the distinctive italic engraved numbers of Kern & Co. of Aarau, Switzerland. It is graduated by quarter-degrees and marked by tens from 10 to 170 both from left to right and from right to left. There are no other marks. The lower edge of the protractor is beveled, with a groove at the origin point.

Ruth E. Crownfield, the widow of Albert C. Crownfield Jr., a mechanical engineer from Mohawk, N.Y., donated this protractor in 1978. The instrument is quite tarnished and scratched, suggesting Crownfield used it frequently. Similar protractors cost $3.50 in the first decade of the 20th century and $4.50 in 1936.